16:330:543            Communication Networks I


Homework 1 (due September 30, 2003)

[20 points]   Prove the correctness of the following protocol, which is a modified version of Stop-and-Wait. Assume that there are three hosts, two of which are senders and one is receiver, sharing the same transmission medium. All hosts can listen to the medium and do so before transmitting any packet. Of course, we assume that all packets are of finite length. Assume an integer number CW, such that:
0 < CWmin £ CW £ CWmax < ¥

NOTE: This is a simplified version of the CSMA/CA protocol used in IEEE 802.11 wireless LANs.

  1. When busy medium is detected, wait with transmission until the medium becomes silent.
  2. When idle medium is detected, select a random number rn Î {0, 1, ..., CW-1} of time units. Decrement rn until it becomes 0. Listen again. If busy, go to 1; if idle, transmit immediately.
  3. If an acknowledgement is not received within a timeout time, double the CW
    CW Ü 2 ´ CW
    If CW > CWmax, set CW Ü CWmax
  4. If an acknowledgement is received, set CW Ü CWmin
HINT: Use the same methodology as in the textbook, Section 2.4

Submission

Only electronic submission will be accepted. The file (Microsoft Word or Adobe PDF must be submitted by 4 p.m. on the due date. The cover page should contain the title: "Communication Networks I -- Homework #1" along with the student's full name and email address. Do not put the social security numbers.

Ivan Marsic
Fri Sep 12 15:39:52 EDT 2003